Aluminum alloy



Patented July 14, 1942 Walter Bonsaclr, South Euclid, Ohio, assignor to The National Smelting Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Original application April 1'1, 1941,

' Serial No. 389,020.

Thi invention relates to alloys, and particularly to aluminum base alloys suitable for casting and working, and having high strength at ordinary and elevated temperatures. I

This application is a division of my copending application Serial No. 389,020, filed April 17, 1 941,

for Aluminum alloys.

It is an object of this invention to produce alloys having relatively high elongation and .relatively high tensile strength.

It is a further objector this invention to provide a relatively light alloy which may be easily cast and machined which may be used at elevated temperatures without 'a rapid deterioration of desirable properties, and which may be readily treated with anodic treatment to give excellent lustre and finish;

It is a still further object of thisinvention to provide an alloy having a relatively high .pro-.

portional limit and relatively high fatigue strength, and in which these properties may be obtained without heat treatment:

It has been found that an aluminum alloy containing iron, and having zinc and magnesium present in proper proportions, will produce an alloy that may be readily cast and have improved physical properties for use both at ordinary anii elevated temperatures, and which may have these properties improved byheat treatment.

When magnesium and zinc are added to aluminumin the proper proportions, a ternary compound of aluminum, magnesium and zinc is formed, which compound is soluble in solid solution in the aluminum. The presence of this compound in relatively small amounts greatly improves the characteristics of aluminum and produc s an alloy having high strength combined ytith high ductility, good casting and forging properties, good color and excellent corrosion resistance. In calculating the amount of magnesium and zinc that should be present in the aluminum alloy to form the desiredpercentage of ternary compound, onlymagnesium which is not combined with silicon is to be calculated, as

it is only such magnesium that is available to combine with zinc-and aluminum to form the ternary compound.

The ternary compound is said by some investigators to have a composition having substantially the formula AlaMgvZne, and other investigators have considered the formula for the ternary compound as being AlzMgaZnz. It will be seen that the amounts of magnesium and zinc relative to each other are quite similar in both formulas and, for the purposes of the improved Divided and this application June 16, 1941, Serial No. 398,314

6 Claims. (Cl. 75-146) alloy, the magnesium and zinc should be present in about the proportion necessary to form the ternary compound of either formula.

An excess of zinc, over and above that which cooperates with magnesium and aluminum ,to form a ternary compound according to the above formula having the greatest proportion of zinc,

increases the brittleness and decreases the ductility of the alloy. For this reason it is undesirable that zinc be present in quantities substantially greater than the amount to react to form such a ternary compound with magnesium and aluminum. The most desirable properties are obtained when the magnesium and'the zinc are proportioned so that the ratio of magnesium (uncombined with any silicon) to zinc is about equal to the ratio represented by the formula AlzMgszna;

or somewhat larger, as represented by the formula AlaMgvZna. A small amount of magnesium may be provided to replenish losses that may occur when the alloy metal is remelted.

Magnesium adds to the hardness and machining qualities of the alloy and, as above stated,

should be present in an amount suflicient to combine with theJzinc and aluminum present. In greater quantities, magnesium tends to make the alloy sluggish, decreasing castability.

Magnesium and zinc have heretofore been added to aluminum in the proportion represented by the formula MgZnz. It has been found, however, that a given percentage ofternary compound is more effective in producing desirable properties, and, because the zinc contentof the ternary alloys is less,'they have a lower density The improved aluminum alloys may have the ternary compoundof aluminum, zinc and magnesium present in an amount ranging from about 2% to 20%, the preferred range being between about 3% and 15%. At room temperature the ternary compound goes into solid solution in aluminum alloys in an amount ,of about 2%.

The percentage in solid solution increases at high temperatures and decreases upon cooling, the excess precipitating out.. Aluminum alloys containing the ternary compound may, therefore, be advantageously heat treated to improve their properties.

A small amount of silicon is usually present in aluminum alloys and from .15% to about 31% is desirable in alloys of the present invention which are to be forged or drawn; more than .7% is frequently desirable in casting alloys. Silicon combines with magnesium in preference to most elements, each part by weight of silicon combiningwith about 1.75%, by weight, of magnesium to formMgaSi. At least suiiicient magnesium is therefore added to the alloy to combine with the silicon uncombined with any calcium to form MgzSi, and, in addition, to combine with all the zinc and form the ternary compound according to theformula AhMgaZm. MgzSi is more stable than the ternary. compound above mentioned and may be maintained in solid solution in aluminum alloys in an amount up to about 1.85%, which is the quantity of MzzSi present if the silicon is present in the alloy, and acts as a hardener, which is sometimes desirable in conjunction with the ternary compound.

MgzSi does not, however, make as efiicient use of' the magnesium as does the above mentioned added. Calcium has an even stronger amnity for silicon than has magnesium and, therefore, it can be used to reduce the amount of silicon available for combination with magnesium. The amount of the relatively expensive magnesium, available for the formation of the ternary compound may thus be increased. Although much more than 1.85% silicide acts as a supplemental'hardener and more. than about 3% or so makes the alloy more sluggish and adversely affects the castability ofthe alloy, up to 3% is desirable, and more than 3% may-gin some cases,-be desirable in the production of hard castings having less intricate shapes, particularly when a large amount of the ternary compormd is present in the alloy. Usual ly, however, the amount of silicon should be between .5% and 1.5%, especially in castings not heat treated. This is true even when calcium is present, although with the latter element more magnesium is available for formation of ,the ternary oompound. It has now been found that aluminum alloys containing magnesium over that necessary to combine with silicon) and'zinc in the proportions to form a ternary compound are greatly improved by the addition of iron and one or more members of the group of hardening elements, consisting of .1% to 1.5% nickel, .1% to 1.5% manganese and O5% to 1% chromium, in a total amount of about .2% or-.3% to 5%, with or without one or more of the grain refining elements selected from the group consisting of titanium, columbium, zirconium, boron, tungsten, molybdenum, tantalum and vanadium, in atotal amount of .005% to .5%.

The alloys of thepresent invention contain iron, magnesium, zinc, silicon, and a total of about .2% to about 5% of one or more hardening or grain refining metals. The magnesium is proportioned to the zinc and silicon so that the magnesium uncombined with silicon is about 35% to about 45% of the zinc. These alloys have an excellent color; high" tensile strength, very high elongation, a high proportional limit and yield strength, and they are exceptional-in that these desirable properties are obtained without heat treatment.

Although the metalsmanganese, chromium and nickel each increase the hardness of the alloy, a given percentage of each 01' these elements improves certain of the properties more than it does others. 'It is therefore preferred that more than one of these elements be present in the alloy. Nickel increases the tensile strength, proportional limit and yield strength of the alloy without decreasing its elongation to any appreciable degree. In fact, with certain amounts of nickel the elongation is increased, so that an alloy having exceedingly desirable and exceptional properties may be obtained.

Alloys containing nickel may be readily heat treated or age hardened togive somewhat superior properties, but very desirable properties which are almost equivalent to the heat treated alloys are also obtained when castings are simply aged at room temperature, with or without quenching from the mold.

" Nickel is quite an effective element in the alloy and appreciable improvements in properties of the alloy are noted when it is present in an amount of about .1%, or more The preferred properties are obtained with about .3% to about .8% or 1% nickel, and in some cases it is desirroom temperature, or when quenched from able to have the nickel present in amounts as great as 1.5%.

Manganese, although it decreases the tensile strength and elongation to some degree, increases the yield strength, hardness and proportional limit of the alloy. It also makes the alloy more corrosion resistant.

Alloys containing manganese may be readily heat treated or age hardened to give somewhat superior properties, but very desirable properties are obtainable when castings are simply aged at mold and aged.

Manganese is a very effective element in the alloy and desirable improvementsare noted when about .1 or even a little less, is present in the alloy. The preferred properties are obtained with about .2% to about .5% or .8% manganese, and

in some cases it is desirable to have the manganese present in amounts as great as'about 1%, or even 1.5%.

Chromium, although it does not appear toimprove the proportional limit and yield strength of the alloy, increases its elongation. It is, therefore, particularly advantageous that both chromium and manganese be present. As little as .05% or .1% chromium, particularly with manganese, is effective in improving properties of the alloy, but .2% or .3% to about .8% or even 1% is desirable. When manganese is also present, the total of manganese and. chromium should preferably be between about .3% and 1.5% of the alloy. When both manganese and chromium are present, they may be in about equal proportions, or preferably with a slightly greater amount of manganese than chromium. 3

The quantity of each of the hardening metals desired ina given alloy also depends somewhat upon the quantity of other hardening ingredients present and upon the amount of ternary compound, a given hardness and tensile strength often being obtainable either with a relatively large amount of strength-improving hardening 'metal and a relatively small amount of ternary compound, or with a, relatively small amount of such metal and a relatively large amount of magnesium and zinc in the proportions of a ternary compound.

the

I pound are relatively difficult a 'ternary compound.

- and metals of the above present in alloys which are to be given a so- As silicon decreases the ductility of the alloy toa substantialdegree, it is best that. when the alloy contains nickel presentinthe upper portion oi the above mentioned range, the silicon not exceed .'7%' or 3%, as thepresence of too much of the hardener Mass! may decrease the ductility to such an extent that the alloy isundesirable for many purposes. Alloys containing nickel andfree magnesium of a ternary compound may contain 1% or 1.5% silicon. While 2% or 3% of the ternary compound of aluminum, magnesium and zinc improves the properties of aluminum or aluminum alloys having low containing such low percentages oi a ternary comto cast. ofthe ternary 'co asmuchas An alloy containing 2% .crease in the amount of ternary compound, and it is, therefore, preferred to have a larger perd zinc in the ratio silicon content, alloys pound may be used for casting purposes. The 'castability, however, is improved with an incentage of the ternary compound present, such I as, 4% to 8% for casting purposes. when the casting is more ,or less intricately shaped, still greater percentages, such as 10% to 15% or of the ternary compound may be present. For alloys to be forged or shaped after casting, the ternary compound should be present in the lower ranges, such as 2% to 8% or so. as the metal is less hard with the lower percentages of the A larger proportion of the ternary compound hardening group may be called solution tre'atment"-than in alloys to be given only an aging treatment, or those to .be

quenched from the casting; mold and .aged at relatively low temperatures. Thus, the desirable properties of the solution heat treated alloys may go obtained when they contain the ternary comound in amounts up to 20% or so, whereas less of the ternary compound, such as (4% to 15%, is preferred'in alloys which are quenched upon removal from the mold and heat' treated at a low temperature, oraged at room temperature.

Iron in suitable amounts further increases the hardness and tensile strength of the alloy without decreasing its ductility a substantial amount. A small amount of iron thus permits one to obtain the properties desired with a smaller amount of magnesium and zinc. These alloys containing ironmay be readily heat treated or age harding elements are aluminum alloy containing present, a given hardnessand tensile strength often being. obtainable with a relatively larger amount of iron and a relatively smaller amount of ternary compound, or a relatively smaller amount of iron and a relatively larger amount of ternary. V

The hardening'elements and the grain refinparticularly desirable in an both iron and the ternary compound. Although the iron itself improves the properties of the alloy, the hardening elements. and the grain refining elements exert a still further improvement independently of iron.

The aluminum alloys of the present invention containing magnesium uncombined with silicon, and zinc in the proportion of a ternary compound, when cast in molds of a design such that chilling takes place substantially simultaneously in the various portions of without the use of grain refining agents and form good castings, However, it has been found that certain grain refining elements substantially improve the properties ofthe aluminum alloy containing the ternary compound, whether or not it contains one or more of the above hardening metals. with or without iron. This is especially true when the metal is cast in molds of more or less intricate shape, where the chilling may not be so uniform throughout the casting.

Grain refiners. whichv improve of the alloy are boron in theamount of .005% to .1%, zircanium in the-amount of .01% to 5%, tungsten in the amount of .01% to .5%, molybdenum in the amount of .01% to 5%, vanadium in the amount of .01% to .5%,'titanium in the amount of .05% to 5%, columbium in the 3 amount of .01% to .5%, and tantalum in the amount of .05% to .5%. Thesegrain refining desirable in the alloys of the present invention,

not all of the grain refiners affect the properties in the same wayi The particular refiner or ened to give somewhat superior properties, but

the iron in combination wth the ternary ele-' ments in the above-proportion is also outstanding, in that almost asdesirable properties are obtained when castings are aged at room temperature' without a heat treatment or quenching.

Iron 'has'generally been considered to crystallime in large platelike crystals, which weaken the I alloy. Iron in the presence of the ternary compound appears to crystallize in finely dispersed form; and the ternary compound also seems to be dispersed, thus producing 'a highly desirable alloy.

Iron in the amount of .4% or more in the alloys of the present invention gives noticeable effects in improving the propertiesof the alloy, and as much as 2% has been found to be desirable for some purposes. 'For most castings it is desirable that the alloy have .6% or 37%. to 1.5% of iron, although about 1% is usually preferred. The quantity of iron desired in the alloy depends also' upon the quantity of other harden ing ingredients and upon the amount of ternary group of refiners selected in any given instance depends upon the particular condition which must be satisfied. The grain refiners selected from the group consisting of titanium, tungsten, molybdenum, zirconium and vanadium, and especially tungsten and molybdenum, improve both the strength and the elongation of the castings. Of these, titanium, being less expensive, is usually. used for ordinary castings, but in cases where the highest elongation, together with strength, is necessary, it is preferred to use tungsten or molybdenum. The grain refiners selected from the group consisting of boron, columbium and tantalum do not appear toappreciably increase the strength or elongation of the alloy, and are usually used where appearance, finish and corrosion resistance are most import- 4 ant, and where strength is of less consequence.

The above described hardening elements, manganese, chromium and. nickel, substantially decrease the hot'shortness, improve the properties of the alloy and assist in maintaining the improved properties at high temperatures, such as are encountered in internal combustion engines. The above grain refining elements, particularly members of the group consisting of tungsten, molybdenum, vanadiumand titanium, also have this property when present in substantial amounts, I

the casting, solidify the properties such as .2% or .3% or so. It is, therefore, especially desirable to have up to .5% or so of these latter elements present when other hardening portional limit of about 17,900 lbs./sq. in., and a yield strength of about 23,900 lbs./sq. in.

When the test bars were simply air-cooled and aged seven days at room temperature, the tensile strength was 40,700 lbs/sq. the elongation was 8.4%, the Rockwell E hardness was 81, the

proportional limit'was 18,600 lbs/sq. in., and the yield strength was 24,100 lbs./sq. in.

Example A similar alloy to that of Example 1, containing only about .25% nickeL'but having the samepercentage of the other ingredients, was chill cast into test bars, air-cooled and aged seven days at room temperature. The test bars had a tensile strength of about 38,400 lbs.-/sq. in., a yield strength of about 23,200 lbs/sq. in., a proportional limit of about 17,700 lbs./sq. in., a hardness of about 82 Rockwell E, and an elongation of about 7.2%.

' Example 3 Test bars-chill cast from an-alloy containing 6% of the ternary compound, about .6% iron, about .25% chromium, and about .5% manganese showed, after quenching and aging for seven days at room temperatures tensile strength of 41,600 lbs./sq. in., a yield' strength of 23,500 lbs./sq. in., a proportional limit of 17,600 lbs./sq. in., an elongation of 9.6%, anda hardness of 80 kg./mm,'.

When bars of the same alloy were simply aircooled and aged for seven days at room temperature, the tensile strength was 41,600 lbs/sq. in.,

the yield strength was 23,500 lbs./sq. in., the proportionallimit was 18,100 lbs./sq. in., the elonga-v tion was about 8%, and the hardness was 82 kg./mm.

When the quantity of manganese in the alloy of Example 3 was increased to about 1%.,the tensile strength of air-cooled test bars, aged for seven days at room temperature, was 38,900 lbs./sq. in., the yield strength was26,600 lbs/sq. in., the proportional limit was 20,100 lbs/sq. in., the elongation was about 5%, and the hardness was 82 kgJmmP.

From the above examples it is seen that evena small proportion of-manganese and chromium markedly increases the tensile strength, proportional limit, yield strength, hardness, and even alloy of outstanding characteristics is produced.' An aluminum base alloy containing 2% silicon and magnesium (uncombined with silicon) and zinc in the proportions represented by the formula AlaMg-zzm, and insumcient amounts to produce 6% of this ternary compound in the alloy, was prepared. From this base alloy three difierent alloys were prepared by incorporating 5 the proportions of iron, indicated in' the following Table 1, and chill cast in standard test bar molds. several bars of each alloy were given the indicated heat treatments, that is, some of the bars of each alloy were removed from the [0 mold while hot and allowed to cool in air, and then aged seven days at room temperature; another set of bars was removed from the mold before the bars had cooled sufllclently to precipitate the hardening ingredients, then quenched in water and allowed to age at room temperature for-seven days.

Table, 1

I Propor- Elonge- Yield Tensile Brinell tion m strength strength hardness Percent Percent Lea/la. Lea/in. LbL/hl. KuJmmJ 1'--." .81 0.2 16,100 23,300 00, 79 2 1.34 4.4 10,200 400 39,6) 85 5 3' 1.87 6.4 18,600 25,311) 39,011) 84 l"- 81 7. 0 10, 400 23, 100 39,400 79 2" 1. 34 5.0 19,400 26,000 41, 100 85 3".. 1.87 6.8 17,40) 213M 40,4(X) 83 Alloy air-cooled; aged at room temperature seven do so 3 "Alloy quenched; aged at room temperature seven It is seen from the test results of the above table that, although the tensile strength may be increased to some'extent by a quenching treat- 35 ment, almost equal results are obtained by simply air-cooling the'casting and aging it at room temperature. Before the quenched casting is aged, a tensile strength of is obtained, while at the has.an elongation of 12%. In an aged casting a tensile strength of even greatr than 40,000 lbs./sq. in., together with an elongation of almost 8%, is obtained. In an aged casting-maximum elongation and substantially maximum strength are obtained when the iron content is about 1% or so.

' When the quantity of ternary compound is increased, these maximum values may be obtainedwith a somewhat lower iron content, or higher maximum strength is obtained with the same iron content; the castability of the alloy may be also somewhat increased. It will be seen that, since the iron permits one to obtain exceptionally high elongation, combined with high tensile strength, without the necessity .of even, as much heat treatment as quenching from the mold, the alloy is especially useful for many purposes, such as large castings or forgings, wherein it is dimcult to heat treat or quench.-

As shown above, iron and the ternary compound alone produce exceptional properties. in an aluminum base alloy, with or without the usual impurities. Even more desirable properties, for some purposes, are obtained with iron and one or more hardening metals of the group consisting of about 41% to 1.5% chromium, about .05% to 1.5% manganese, and about .1% to 1.5%

nickel. As little as a total of about .1% or .2% of these hardening metals is efl'ective in improving the iron ternary aluminum alloy, but about .4% or .5% to about 1.5% of these hardening metals is preferred, and even 2% is desirable for many applications. The iron may be present in the amounts above set forth, but less than about 75 1.5% is preferred.

over 30,000 lbs./sq. in. same time the casting elongation was 4.5%.

. um, about .2% titanium,

= An aluminum base The renewing examples illustrate the eflect or these elements on an alloy containin 7 I Example 4 An alloysimilai. to the alloy 01 Example 1, but'containing .4% manganese (instead oi. .4%, nickel) and 1% iron, when 011111 0880 into but bars, quenched anda'ged' seven' days at room 1 temperature, had a tensile strength or 89,800 'lbsJsq. in., a yield strength 01 about 25,200

lbs/sq. in., a proportional limit oi 18,600 lbsJsq. in., a hardness or about 82 Rockwell E, and an elongation of about 5.7%; when the bars weresimply air-cooled and aged as above. the tensile strength was 37,700 lbs./sq. in., the yield strength was 25,0001bs./sq. in., the proportional limit was. 19,200 lbsJsq. in., the hardnws was 81, and the V Example 5' An aluminum base alloy containingabout 6% or the above ternary compound, based on the formula AhMB'IZm, about 1% iron, about 3% silicon, and about .2% manganese was chill cast into test bars, quenched, and aged seven days at room temperature. when tested, these test bars showed a tensile strength 01 about 40,500 lbs/sq. in., a yield strength 01 about 23,300 lbs./sq. in., a proportional limit 01 about 18,000 lbs/sq. in., a

hardness or about 81 Rockwell E, and an elonga- 80 tion of 7.8%.

Example 6 An aluminum bi se alloy containing about .6% iron, about .3% manganese, about .2% chromimagnesium' in proportion to combine with the silicon and to tom 6% ot the ternary compound AlaMgqZnc, with the balance substantially aluminum and minor impurities, was prepared and chill cast into test bars, quenched and aged seven days at room temperature. when tested, they showed a tensile strength 01 42,300 lbs. /sq. in., an elongation of 10.3%, a yield strength oi 24,300' 1bs./ sq. in., a proportional limit of 18,100 Y lbs/sq. in., and a Rockwell hardness 01-81.

When the castings were simply air-cooled and aged seven days at room temperature, the tensile.

' strength was 41,000 lbs/sq. in., the yield strength 7 was 24,500 lbs.lsq. in., the proportional limit was 19,000 lbs./sq. in., the hardness was '80 Rockwell 0 E, and the elongation was 8.5%.

, Example 7 7 ,An aluminum base alloy containingabout .45%

manganese, about .6% iron, about .15% silicon,

about .2% titanium, and about 6% or a ternary compound. (based on the iormula AhMSrZ-m), with the balance substantially all aluminum and minor impuritieawas prepared and chill cast into test bars or standard shape. were quenched from the mold and aged at room temperature ior seven days. Whentested, the bars showed a tensile strength 01 about 39,800 lbs./sq. in., a proportional limit or about 17,100

lbs/sq. in., a yild-s'trength of about 23,200 5 lbs/sq. in., a hardness 01- about 81 RockwellE,

and an elongation 01 about 7.9%.

Example 8 alloy identical alloy oi Example 7., with-the exception that it contained about 1.2% manganese (instead oi 145%) was prepared and chill cast into test bars, quenched and aged seven days atroomtempcranary compound or about .2% silicon, and 35 vanadium instead I t The test bars with the Thevfollowing p 0, a tensile strength 1 about 37,500 lbsJsq. in., a

proportionallimit 01 about 10,400 lbs./sq. in., e

Example 9 1 An aluminum basealloy containing about .2% silicon, magnesium uncombined with silicon and zinc in proportions to form about 6% of the teraluminum. magnesium and zinc according to the formula AlzMgaZm, and containing about 1% iron and about .2% of the grain refiner, titanium, was chill cast into test bars, which were removed from the mold before they reached precipitation temperature, quenched in water and aged seven days at room temperature. tensile strength of 41,600 lbs/sq. in., a yield strength of 24,500 lbs./sq. in., a proportional limit of 18,000 lbs/sq. in., an elongation of 8%, and a hardness of 83. 1

Example 10 silicon, about .6% iron, about 6% of the above described ternary compound, and about-.05% columbiu-m, was chill cast into test bars, which were air-cooled and aged-seven days at room temperature. when tested, these bars had a tensile strength of 36,100 lbs/sq. in., a yield strength of 21,700 lbs/sq. in., a proportional limit of 16,400 lbs/sq, in., an elongation of a hardness of 77, and a iine grain'structure. Y

Example 11 An aluminum base alloy containing about 6 of the ternary compound, about 3% manganese, about .25% chromium, about .2% silicon, and about .3% tungsten was chill cast into test bars which were quenched and aged three hours at C. When tested, these bars had a tensile strength of 40,600 lbs/sq. in., a yield strength of 25,800 lbs/sq. in., a proportional limit of 16,500 lbs ./sq. in., and an elongation of 13.2%, and a hardness'of 76 Rockwell E. When the chill cast bars were quenched and aged seven days at room temperature, they had a tensile strength or 43,300 lbs./sq. in., a yield strength of 26,500

lbs./sq. in., a proportional limit of 18,400 lbs/sq.

in., and elongation of 13%, 79 Rockwell E.

when the grain refiner and a hardness of in the above example is omitted, the tensile strength and elongation are lower and the castability is decreased.

Example 12 v w I when the alloy of Ex I ple 11 contained .03% gsten, the test bars which were chill cast, quenched and aged seven days at room temperature had a hardness of 74, an elongation of'8.7'%, a proportionallimit of 16,500 lbs/sq. in., a yield strength of 24,900 lbs./sq. in., and a tensile strength of 38,800 lbs./sq.'

in. When the percentage of vanadium was increased to .l5,%, the hardness was 80, the elongation was 8.5%, the proportional limit was 17,700 lbs./sq. in., the-yield strength was 25,500 'lbsJsq. in., and the tensile strength was 40,400 lbs./sq in. 1

P v Example 13 when, in the alloy of Example 11, the tungsten was substituted 'by .06% molybdenum, the elonoperties were'obtained:

These bars, when tested, had a 6 7 gation 'of the test bars which were chill cast, quenched and aged seven days at room temperature was 11.2%, the proportional limit was 18,100 lbs/sq. in., the yield strength was 25,800

of 24,500 lbs/sq. in, and a tensile strength of 41,400 lbsJsq. in.

Example 14 when, in the alloy of Example 11, .05% airconium was used instead of the tungsten, the elongation'p'f the test bars which ware chill cast, quenched and aged seven days at room temperature was 12.6%, the tensile strength was 42,300 lbs/sq. in., the yield strength was 26,000 lbs/sq. in'., the proportional limit was 17,600 lbs/sq. in., and the hardness was 80 Rockwell E. Since the molecular proportion of zinc is never more than the molecular proportion of the relatively light magnesium in the ternary compound, it is seen that, in addition to high strength, the alloys are light in weight and are, therefore, especially adapted to aircraft construction'and the like. I quantity of ternary compound is sufflciently low,

, so that the alloy may be drawn or rolledinto structural members.

If the alloy contains uncombined silicon, about This is particularly true when the of course, be obtained relatively quickly by aging 1.75% magnesium is required to combine with each percent of uncombined silicon to form magnesium silicide (M8351) before any ternary com pound will be formed. For example, if 2% of the ternary compound on the basis of AhMgaZna be desired in an alloy having 3% silicon, the

amountof magnesium to be addedto form the ternary compound will be .45%, or about .5%, and the magnesium to combine with .3% silicon will be about .5%, making a total of about 1%. The magnesium and mom an alloy containing .-7 free silicon and 20% AlaMg'zZns would be about 7% and 12%, respectively. The alloys described herein include aluminum, magnesium of 1.2% to 12% of the alloy, and the magnesium, uncombined with silicon, being proportioned to the zinc in the ranges of the formulas given for the ternary compound. The proportions for the formation of the ternary compound in the alloy exist when the magnesium is about 35% tq 45% of the zinc content plus 175% of the silicon content. Most desirable properties may be obtainedwhen the magnesium (uncombined with silicon) I is in the lower portion of this range, or about- 35% to 40% of the zinc.

In the above examples of alloys of the. pres- I loys, namely, that the tensile strength may increase up to approximately 50% of itsinitiah value by aging at room temperature for relatively long periods of time, such as a'few months. The same improvement in tensile strength can,

- and zinc, the zinc being present in the amounts and tested after aging at temperatures above room temperature. The improvement of properties is illustrated y the following table showing the improvement in an alloy containing a small percentage of silicon, about 6% ternary compound, about 1% iron, and about .2% titanium. The test bars were chill cast, quenched from the mold,

the period indicated.

Table 2 Aging time Elongation 3: 35 fiaifi Percent None 12 31, 200 66 8 days-. 7.0 30,700 76 1 week. 7. 3 38, 300 80 2weeks ac 39,700 82 3 weeks 6. 6 40, 000 84 4 weeks 0. 3 40, 300 83 5 weeks 6. 6 40, 000 85 2 months-- ii. 0 v 41, 350 85. l 3 months 4. 8 41, 600 88. 6 4 months.. 4. 8 42, 500 87. 6 6 months" 6. 2 43, 400 89. l 6 months 6. 1 43, 700 89. i

To obtain these exceptional properties in aluminum base alloys commonly in use one has to resort to a solution and aging heat treatment, whereas in alloys of thepresent invention it is not necessary to solution heat treat for improvement in properties. J I

The alloys of the present invention have good I fatigue and tensile strengthand a relatively high proportional limit, even at relatively high temperatures; they may be heat treated to improve and modify their properties; and they have sufllcient ductility and hardness so that they can be used as sheets, rods, wire, structural shapes, castings, machine parts, etc. These alloys have a desirable color, high corrosion resistance, and may be anodically finished or highly polished with excellent results, and are suitable for many uses, among them being the production of castings which are shaped or formed to some extent after casting. The. alloys having the lower percentages of ternary compound may even be forged at'room temperature, and are thus useful for many special purposes.

It is to be understood that, in considering the amount of zinc and magnesium to add to aluminum alloys to form the ternary compound of aluminum, magnesium and zinc in the alloy, such magnesium as is necessary to combine with the uncombined silicon is" not to be considered as part of the magnesium necessary to form the specified amount of ternary compound.

,tion' heat treatment.

My copending application Serial No. 389,020 and related copending applications are directed to an alloy similar in composition to that claimed herein, but containing copper, which functions in a somewhat different manner than do the hardening or this application. Due to the fact that copper is considerably more soluble at high temperatures than at low, it acts as a precipitation ingredient, so that articles made from alloys containing are benefited more by solution heat treatment.

In .the present application, on the other hand, the constituents have considerably less solid solubilityat higher temperatures, and yet give' excellent strengths and" ductility without 'solu- It is to be understood that the particular compounds disclosed and the procedure set forth are at room temperature for 4 grain refining metals included. in

2,290,017 presented for-purposes of explanation and illustration, and that various equivalents can be used, and modifications of said procedure can be made, without departing from my invention as defined in the appended claims.

What I claim is: v

1. An aluminum alloy containing magnesium, zinc, about .-i% to 2% iron, silicon in an amount upto 1.5%, and wear more metals of the hardeners and grain refiners to increase strength, ductility or hardness of the alloy, with minor impurities, the amount of zinc in the alloy being about 1.2% to 12%, and the amount of magnesium in the alloy uncombined with the silicon being about 35% to 45% of the zinc content, the total magnesium being within the range of about .5% to 7%, e

the balance substantially all aluminum and 2. An aluminum alloy containing magnesium,

'zinc, about .4% to 2% iron, silicon in an amount up to 1.5%, and one or. more metals of the hardeners and grain refiners to increase strength, ductility or hardness of the alloy, no

one of such metals being present in amounts more than 1.5%, with the balance substantially all aluminum and minor impurities, the amount of zinc in the alloy being about 1.2% to 12%, and the'amount of magnesium in the alloy un-. combined with the silicon being about 35% to 45% of the zinc content, the total magnesium being within the range of about .5% to 7%.

3. The alloy set forth in claim 1 in whichthe zinc content is about 1.2% to 6% and the magnesium content is within the range of about .5% to 6%.

4. The alloy set forth in claim 1 in which the zinc content is about 1.2% to 4.8% and the 

